But when it comes to the taboo topic of royalty, neighboring Thailand is starting to catch up. Dozens of activists, bloggers, and other citizens have fallen foul of a criminal law on royal libel known as lèse-majesté. Censors have stepped up surveillance of the Internet and snooped on chatrooms.

In April, an engineer was sentenced to 10 years in jail for posting video on YouTube that was deemed offensive. In January, an Australian author was convicted over a passage about a Thai prince in an obscure novel, but was later pardoned and released. Other similar cases are under police investigation.

Thailand’s constitutional monarchy has long been held in high esteem by its subjects. But a protracted political crisis has begun to erode taboos against frank discussions of royals and the palace's role in public life.

In response, authorities have stepped up efforts to enforce the draconian lèse-majesté law. The crisis has been exacerbated by concerns over the passing of King Bhumibol Adulyadej, the world’s longest-serving monarch, and a possibly destabilizing succession.

Daranee belongs to the red-shirt political camp aligned to former Prime Minister Thaksin Shinawatra, who was ousted by a military coup in 2006. Opponents accuse Mr. Thaksin of plotting against the crown, which he denies.

Daranee’s speeches were delivered at a public park where political rallies are often held. A red-shirt rally is due to take place this weekend in Bangkok, prompting the government to invoke a tough security law.

In fact, her most inflammatory speech was a wide-ranging attack on the 2006 military coup makers and their conservative allies. It drew parallels between Thailand and the fate of royal regimes in France and Nepal.

By the standards of Thai political rhetoric, it was extremely strong stuff. Enough to turn Daranee into Thailand’s latest political prisoner. She probably won’t be the last.